Ceramic sintering materials in which the principal component comprises alumina, zirconia, silicon nitride, and silicon carbide, etc. have high strength, high hardness, excellent heat resistance, and an excellent anticorrosive property. Thus, these ceramic materials are useful in a variety of applications.
Of many ceramic sintering materials conventionally available, zirconia sintering materials are especially useful in areas that require excellent mechanical strength and sliding characteristics. In particular, zirconia sintering materials are often used in mechanical device parts where great resistance to wear is required. Some of the applications for zirconia sintering materials include, but are not limited to, a conveying arm and a pincette for gripping a wafer in a semiconductor manufacturing device; a separating claw used in an image forming apparatus, such as a printer, etc.; and a tape guide used to convey and guide a tape-shaped material, such as a magnetic tape, etc. In these and many other applications, zirconia sintering materials also need to avoid excessive static electricity accumulation and rapid discharge of static electricity.
Unmodified zirconia materials have excellent mechanical characteristics but are typically also good electric insulators. Therefore, most mechanical parts or items made from unmodified zirconia materials are unable to safely dissipate static electricity and often result in arcing from the static electricity that is built-up. Often this static electricity arcing can severely damage electronic components within the device, a magnetic recording media or other materials on which the parts are used.
One can reduce the amount of static electricity build-up within the sintered zirconia material by adding a conductive additive to increase the electricity conductivity of the sintered zirconia material. Unfortunately, the addition of conductivity additive can create problems as well. For example, if the sintered zirconia material is excessively conductive, it can induce arcing between a charged object and the conductive sintered zirconia part. In addition, excessive addition of the conductive additive degrades the favorable mechanical properties of the sintered zirconia material.
U.S. Pat. No. 6,274,524 discusses a semiconductive zirconia sintering body which overcomes some of the problems associated with many conventional zirconia sintering bodies. The semiconductive zirconia sintering body discussed in U.S. Pat. No. 6,274,524 is purportedly able to discharge static electricity “at suitable speed without greatly reducing mechanical characteristics of zirconia.” See the Abstract. However, the zirconia sintering material in U.S. Pat. No. 6,274,524 requires a relatively pure raw material powder (i.e., zirconia). In particular, U.S. Pat. No. 6,274,524 states that impurities such as “Al2O3, MnO, SiO2, Na, Fe, etc. can be included in the raw material powder if these impurities have a weight % equal to or smaller than 2.0.” See, for example, Col. 3, lines 29-33. Use of such a high purity raw material powder inherently increases the cost of the zirconia sintering material.
Therefore, there is a need for a semiconductive zirconia sintering material which does not require such a low impurity content requirement yet offers a substantially similar or better mechanical properties as currently available zirconia sintering materials.